The present invention relates to mixed powder comprising noble metal powder and oxide powder to be used as a raw material upon producing a target of a component containing noble metal and oxide, and to its production method, and in particular relates to a method of inexpensively producing mixed powder comprising noble metal powder and oxide powder, and the obtained mixed powder comprising noble metal powder and oxide powder
A target of a component containing noble metal and oxide as represented with a (Co—Cr—Pt)+SiO2 target is being used as a sputtering target for a recording layer of a magnetic recording medium. In order to produce this target, noble metal powder (fine powder) is required.
The conventional method of producing noble metal fine powder is as follows when taking platinum as an example. Foremost, a platinum raw material (for instance, platinum scrap) is dissolved in royal water, and the residue that did not dissolve in the royal water is filtered and removed. After the filtering and removal process, this is heated in order to denitrate nitric acid from the royal water to obtain a chloroplatinic aqueous solution. Subsequently, this is reacted with ammonium chloride to obtain a solid ammonium chloroplatinate. Moreover, the ammonium chloroplatinate is roasted to desorb ammonium chloride, whereby obtained is sponge-like platinum.
Subsequently, the sponge-like platinum is once again dissolved in royal water to obtain a chloroplatinic aqueous solution, pH in the liquid is adjusted to be neutral to alkaline, and platinum is deposited based on the reduction reaction of adding hydrazine.
The foregoing platinum can be made into fine powder by adjusting the reduction reaction conditions, and the intended fine platinum powder can be produced through the processes of filtering and removal, cleaning and drying.
In the foregoing process, the processes from “sponge-like platinum is once again dissolved in royal water” onward are the processes for producing the fine platinum powder, and entail increased costs.
In addition, there is also a problem in that the chlorine contained in the royal water and nitrogen responsible for the hydrazine reduction reaction will remain as impurities in the fine platinum powder. The processes of heating and drying are required for sufficiently eliminating the foregoing impurities, and if the condition is set to a high temperature, grain growth and aggregation will occur.
Powder that was subject to grain growth or aggregation during the drying process as described above will further require the pulverization and classification processes. Meanwhile, if low temperature drying is performed, since degassing will be insufficient, not only will the warm-water cleaning and re-drying processes become required, although this will have some effect on the chlorine, there will hardly be any effect on the nitrogen. Thus, the conventional process has a problem that the production cost for obtaining fine powder of noble metals becomes high.
Moreover, as a similar method of producing platinum powder, disclosed is a method of producing platinum powder by simultaneously adding chloroplatinic aqueous solution and ammonia hydrazine aqueous solution in an ammoniacal aqueous solution (refer to Patent Document 1).
In the foregoing case, the method of producing the powder in a solution is being adopted. Consequently, the obtained platinum powder must be subject to suction filtration, subsequently dried, further baked at 350 to 600° C., and gas components such as chlorine adsorbed on the platinum powder must be removed.
Moreover, in order to perform dechlorination, the processes of warm-water cleaning, drying, and pulverization are required.
Since the foregoing processes are indispensible for reactions in a solution, the processes become much more complicated and push up the production cost.
As a similar method of producing platinum powder, disclosed is a method of producing platinum powder by simultaneously adding an ammonia hydrazine aqueous solution in the chloroplatinic aqueous solution (Patent Document 2).
In the foregoing case also, the method of producing the powder in a solution is being adopted. Consequently, the obtained platinum powder must be cleaned, subject to suction filtration, and subsequently dried, but the foregoing processes alone will not be able to sufficiently eliminate the chlorine and nitrogen remaining as impurities in the platinum powder.
The processes of heating and drying are required for sufficiently eliminating the foregoing impurities, and if the condition is set to a high temperature, grain growth and aggregation will occur. Powder that was subject to grain growth or aggregation during the drying process as described above will further require the pulverization and classification processes. Thus, the processes become much more complicated and cause the production cost to increase.    [Patent Document 1] Japanese Published Unexamined Application No. 2008-95174    [Patent Document 2] Japanese Published Unexamined Application No. H02-294416